The present disclosure relates to release layers, and more specifically, to low surface tension aqueous solutions, such as fountain solutions, which operate as release layers. More particularly, the embodiments pertain to the aforementioned release layers and their integration into copying and printing machines, such as inkjet machines, multifunctional devices, color systems, and the like, wherein the release layers can be incorporated onto a hydrophilic roll material for contact leveling of UV curable gel inks.
Lithographic, flexographic, and gravure printing techniques have been known for many years. The basic principle of lithography is transferring ink from a surface having both ink-receptive and ink-repellent areas that comprise an image. Offset printing incorporates an intermediate transfer of the ink. In offset printing, an offset lithographic press transfers ink from a plate on a rotating cylinder to a rubber blanket cylinder, and then the blanket cylinder transfers the image to a substrate, which may be either a cut sheet or a web substrate. In flexographic printing, the ink is picked up in ink pockets on an anilox roll and transferred to a rubber plate having raised image areas that is mounted on a rotating cylinder. The flexographic plate then transfers the image to a sheet or web substrate. In gravure printing, engraved ink wells are arranged on a cylinder to form an image. When the ink wells contain ink and make direct contact with a sheet or web substrate, an ink image is transferred from the cylinder onto the substrate. The flexographic and gravure methods are especially useful for printing onto a web of film or foil material.
Ink jet printing systems often use either a direct printing architecture or an offset printing architecture. In a direct printing system, ink is ejected from jets in the printhead directly onto the final receiving web or substrate such as paper. In an offset printing system, the image is formed on an intermediate transfer surface and subsequently transferred to the final receiving substrate such as a web or individual substrate such as paper.
U.S. Patent Application Publication No. 2009/0141110, which is hereby incorporated by reference herein in its entirety, discloses a printing apparatus, including a) a printing station with at least one printhead for applying phase change ink to a substrate in a phase-change ink image, and b) an ink spreading station including a heated or unheated ink spreading member and a back-up pressure member in pressure contact with the ink spreading member, and wherein a nip is formed between the ink spreading member and the back-up pressure member for spreading the phase change ink image on the substrate, wherein said substrate is passed through the nip, and wherein the pressure member includes i) a substrate, and ii) an outer coating having a polymer matrix with an oleophobic resin, a fluoropolymer lubricant, and a first additive.
U.S. Patent Application Publication No. 2009/0142112, which is hereby totally incorporated by reference herein in its entirety, discloses an offset printing apparatus for transferring and optionally fixing a phase change ink onto a print medium including a) a phase change ink application component for applying a phase change ink in a phase change ink image to an imaging member; b) an imaging member for accepting, transferring and optionally fixing the phase change ink image to the print medium, the imaging member having: i) an imaging substrate, and thereover ii) an outer coating comprising a polymer matrix with an oleophobic resin, a fluoropolymer lubricant, and a first additive, and c) a release agent management system for supplying a release agent to the imaging member wherein an amount of release agent needed for transfer and optionally fixing the phase change ink image is reduced.
Regardless of the printing system that is being employed, there are many known printing applications for these systems that utilize heat-curable compositions. In these printing applications, the desired image, text or logo is applied to a substrate and then thermally cured. Typically, such heat curable compositions require the use of organic solvents that contain a significant amount of volatile organic compounds (VOCs). These VOCs escape into the atmosphere while the heat curable coating dries. As a result, these solvent based systems can be undesirable due to the environmental hazards and expenses associated with VOCs, such as water and air pollution and related expenses, namely the cost of complying with strict government regulations with respect to solvent emission levels.
In contrast, UV curable ink compositions contain reactive monomers instead of solvents, thereby eliminating many of the detrimental effects associated with VOCs. Another advantage to using UV curable ink compositions includes a typically high production rate for UV cure reactors. In particular, cross-linking of UV ink can occur in milliseconds, depending upon the color of the ink and the intensity of the UV light source. These advantages and various others have placed significant attention on UV inks as a significant player in future generations of printing technology
Phase change inks, such as UV curable gel inks, are in the gel phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of ink drops. UV curable gel ink is typically jetted at a temperature of about 75° C. and has a melt viscosity at the jetting temperature of approximately 10 centipoise.
UV curable gel inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping and have long term storage capabilities, among other reasons. In addition, problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated with UV curable gel inks, thereby improving the reliability of the ink jet printing. Furthermore, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (such as, for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Nevertheless, gel inks require some type of transformation such as curing to prevent them from running or smearing when printed onto a substrate and subjected to general handling. In addition, uncured gel inks stick to roller surfaces in print paths, making them unsuitable for many printing applications without some sort of transformation or curing.
Furthermore, while gel ink enables printing onto porous substrates, it unfortunately has also been observed to exhibit microbanding. Microbanding is an uneven distribution of ink in an image area in which the image should be smooth and uniform. Because the ink temperature drops after ejection, the ink freezes on contact with the substrate and an uneven distribution of ink on the image substrate may occur. The human eye can sometimes observe the uneven distribution as bands or lines in the direction of the substrate travel past the print head. This uneven distribution might be addressed by leveling the ink on the image substrate with a contact member, such as a roller, belt, or wiper, in an effort to normalize the ink distribution. Also leveling enables uniform gloss for better image quality, and facilitates line growth to compensate for missing or weak jetting.
For at least the reason that gel inks typically have a mayonnaise-like consistency, they also have very little cohesive strength prior to curing. In addition, gel inks are typically designed to have good affinity to many different types of materials. What this means is that that conventional methods for flattening a layer of ink tend to fail with respect to gel inks, because the gel ink splits. As the splitting occurs, the gel ink leaves a significant portion of the image behind on the device that is trying to flatten it, such as a traditional fuser roll typically used in xerography processes.
Thus, there is a desire to have the ink leveled prior to having it UV cured so that a more uniform gloss can be achieved, missing jets can be masked, and because certain applications such as packaging require thin layers of relatively constant thickness. Methods or means to prevent the occurrence of microbanding, ink splitting and ink offset would be beneficial.
In particular, one of the primary challenges relating to preventing the occurrence of ink splitting, offset or microbanding has been to identify and fabricate appropriate leveling surfaces or coatings that are capable of contacting a UV gel image in order to level the image, while remaining suitably ink-phobic in order to prevent ink offset to the contact leveling surface.
Typical approaches to addressing ink offset, ink splitting, microbanding and to improving image quality and gloss, particularly for UV curable gel inks, and in addition to those already mentioned include improving ink cohesion through changes in ink formulation or through partial curing. Another alternate approach involves using a thin low cohesion release layer placed between the leveling surface and the ink patch, whereby upon contact and separation between the ink patch and the release layer coated leveling surface, the lower cohesion release layer splits instead of the ink layer.
Thus, while known approaches are suitable for their intended purposes, a need still remains for improved contact leveling and release layers that can achieve offset free leveling, eliminate or significantly reduce the occurrence of ink splitting and/or microbanding, all while improving overall image quality and gloss.